Magnetic field sensors, i.e., circuits that use magnetic field sensing elements, are used in a variety of applications, including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example magnetic domains of a ring magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.
Magnetic field sensors employ a variety of types of magnetic field sensing elements, for example, Hall effect elements and magnetoresistance elements, often coupled to a variety of electronics, all disposed over a common substrate. A magnetic field sensing element (and a magnetic field sensor) can be characterized by a variety of performance characteristics, one of which is a sensitivity, which can be expressed in terms of an output signal amplitude versus a magnetic field to which the magnetic field sensing element is exposed.
The sensitivity of a magnetic field sensing element, and therefore, of a magnetic field sensor, is known to change in relation to a number of parameters. For example, the sensitivity can change in relation to a change in temperature of the magnetic field sensing element. For another example, the sensitivity can change in relation to a strain imposed upon the substrate over which the magnetic field sensing element is disposed. Such a strain can be imposed upon the substrate at the time of manufacture of an integrated circuit containing the substrate. For example, the strain can be imposed by stresses caused by curing of molding compounds used to form an encapsulation of the substrate, e.g., a plastic encapsulation.
It will be recognized that changes in the temperature of a magnetic field sensor can directly result in changes of sensitivity due to the changes of temperature. However, the changes in the temperature of the magnetic field sensor can also indirectly result in changes of sensitivity where the temperature imparts strains upon the substrate over which the magnetic field sensing element is disposed. The changes in sensitivity of the magnetic field sensor and of the magnetic field sensing element are undesirable.
As is known, some integrated circuits have internal built-in self-test (BIST) capabilities. A built-in self-test is a function that can verify all or a portion of the internal functionality of an integrated circuit. Some types of integrated circuits have built-in self-test circuits built directly onto the integrated circuit die. Typically, the built-in self-test is activated by external means, for example, a signal communicated from outside the integrated circuit to dedicated pins or ports on the integrated circuit. Alternatively, in some circuits, built-in self-test is activated by internal means, for example, by an on-chip coil or the like is used to generate a self-test magnetic field, as described in a U.S. Pat. No. 8,447,556, entitled “Circuits and Methods for Generating a Self-Test of a Magnetic Field Sensor, which patent is assigned to the assignee of the present application and incorporated herein by reference in its entirety.
Some magnetic field sensors employ self-calibration techniques, for example, by locally generating a calibration magnetic field with a coil or the like, measuring a signal resulting from the calibration magnetic field, and feeding back a signal related to the resulting signal to control a gain of the magnetic field sensor. Several self-calibration arrangements are shown and described in U.S. Pat. No. 7,923,996, entitled “Magnetic Field Sensor with Automatic Sensitivity Adjustment” and U.S. Pat. No. 8,680,846, entitled “Circuits and Methods for Self-Calibrating or Self-Testing a Magnetic Field Sensor,” both of which are assigned to the assignee of the present invention. Also U.S. Pat. No. 8,542,010, entitled “Circuits and Methods for Generating a Diagnostic Mode of Operation in A Magnetic Field Sensor” and assigned to the assignee of the present invention, teaches various arrangements of coils and conductors disposed proximate to magnetic field sensing elements and used to generate a self-test magnetic field. The above application also teaches various multiplexing arrangements. These applications, and all other patents and patent applications described herein, are incorporated by reference herein in their entirety.